Systems and methods for improving efficiency of electrosurgical generators

ABSTRACT

A method of improving efficiency of an electrosurgical generator is presented, the method including controlling an output of an electrosurgical generator by converting a direct current (DC) to an alternating current (AC) using an inverter, and sensing a current and a voltage at an output of the inverter. The method further includes the steps of determining a power level based on the sensed voltage and the sensed current, determining an efficiency of the electrosurgical generator, and inserting a predetermined integer number of off cycles when the efficiency of the electrosurgical generator reaches a threshold power efficiency.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to U.S.Provisional Application Nos. 61/881,547 and 61/881,575, both filed onSep. 24, 2013, the entire contents of which are hereby incorporatedherein by reference. The present application is related to U.S. patentapplication Ser. No. 14/320,804 filed on Jul. 1, 2014.

BACKGROUND

1. Technical Field

The present disclosure relates to electrosurgery. More particularly, thepresent disclosure relates to systems and methods for improvingefficiency of electrosurgical generators.

Background of Related Art

Electrosurgery involves the application of high-frequency electriccurrent to cut or modify biological tissue during an electrosurgicalprocedure. Electrosurgery is performed using an electrosurgicalgenerator, an active electrode, and a return electrode. Theelectrosurgical generator (also referred to as a power supply orwaveform generator) generates an alternating current (AC), which isapplied to a patient's tissue through the active electrode and isreturned to the electrosurgical generator through the return electrode.The AC typically has a frequency above 100 kilohertz (kHz) to avoidmuscle and/or nerve stimulation.

During electrosurgery, the AC generated by the electrosurgical generatoris conducted through tissue disposed between the active and returnelectrodes. The tissue's impedance converts the electrical energy (alsoreferred to as electrosurgical energy) associated with the AC into heat,which causes the tissue temperature to rise. The electrosurgicalgenerator controls the heating of the tissue by controlling the electricpower (i.e., electrical energy per time) provided to the tissue.Although many other variables affect the total heating of the tissue,increased current density usually leads to increased heating. Theelectrosurgical energy is typically used for cutting, dissecting,ablating, coagulating, and/or sealing tissue.

The two basic types of electrosurgery employed are monopolar and bipolarelectrosurgery. Both of these types of electrosurgery use an activeelectrode and a return electrode. In bipolar electrosurgery, thesurgical instrument includes an active electrode and a return electrodeon the same instrument or in very close proximity to one another,usually causing current to flow through a small amount of tissue. Inmonopolar electrosurgery, the return electrode is located elsewhere onthe patient's body and is typically not a part of the electrosurgicalinstrument itself. In monopolar electrosurgery, the return electrode ispart of a device usually referred to as a return pad.

Some electrosurgical generators include a controller that controls thepower delivered to the tissue over some period of time based uponmeasurements of the voltage and current near the output of theelectrosurgical generator. These generators use a discrete Fouriertransform (DFT) or polyphase demodulation to calculate the phasedifference between measurements of the voltage and current forcalculating real power and for performing calibration and compensation.

However, at low power levels, some electrosurgical generators exhibitlow efficiencies. Thus, there is a need for improved methods ofmaintaining the efficiency of electrosurgical generators.

SUMMARY

A method for controlling an output of an electrosurgical generatorincludes the steps of converting a direct current (DC) to an alternatingcurrent (AC) using an inverter, and sensing a current and a voltage atan output of the inverter. The method further includes the steps ofdetermining a power level based on the sensed voltage and the sensedcurrent, determining an efficiency of the electrosurgical generator, andinserting a predetermined integer number of off cycles when theefficiency of the electrosurgical generator reaches a threshold powerefficiency.

According to a further aspect of the present disclosure, anelectrosurgical generator includes a radio frequency (RF) amplifiercoupled to an electrical energy source and configured to generateelectrosurgical energy, the RF amplifier including: an inverterconfigured to convert a direct current (DC) to an alternating current.The electrosurgical generator further includes a plurality of sensorsconfigured to sense voltage and current of the generated electrosurgicalenergy and a controller coupled to the RF amplifier and the plurality ofsensors. The generator may further determine a power level based on thesensed voltage and the sensed current, determine an efficiency of theelectrosurgical generator, and insert a predetermined integer number ofoff cycles when the efficiency of the electrosurgical generator reachesa threshold power efficiency.

According to another aspect of the present disclosure a method ofimproving efficiency of an electrosurgical generator includesdetermining power levels based on sensed voltage and sensed current,determining an efficiency of the electrosurgical generator based on thedetected power levels, and gradually dropping a predetermined integernumber of output or off cycles when the efficiency of theelectrosurgical generator reaches a threshold power efficiency, thepredetermined integer number of output or off cycles being randomizedvia a random number generator.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described withreference to the accompanying drawings wherein:

FIG. 1 is an illustration of an electrosurgical system including agenerator, in accordance with embodiments of the present disclosure;

FIG. 2A is a block diagram of an electrosurgical system includinggenerator circuitry according to a combination of a modified-Kahntechnique and a Class S generator topology, in accordance with oneembodiment of the present disclosure;

FIG. 2B is a block diagram of an electrosurgical system includinggenerator circuitry according to the modified-Kahn technique, inaccordance with another embodiment of the present disclosure;

FIG. 2C is a block diagram of an electrosurgical system includinggenerator circuitry according to the Class S device topology, inaccordance with still another embodiment of the present disclosure;

FIG. 3 a schematic block diagram of a controller of the generatorcircuitry of FIG. 2A, in accordance with an embodiment of the presentdisclosure;

FIG. 4 is a circuit diagram illustrating switching in different resonantcomponents, in accordance with an embodiment of the present disclosure;and

FIGS. 5A and 5B are graphs illustrating insertion of output cycles atpredetermined time periods, in accordance with an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an electrosurgical system 100 in accordance withembodiments of the present disclosure. The electrosurgical system 100includes an electrosurgical generator 110 which generateselectrosurgical energy to treat tissue of a patient. The electrosurgicalgenerator 110 generates an appropriate level of electrosurgical energybased on the selected mode of operation (e.g., cutting, coagulating,ablating, or sealing) and/or the sensed voltage and current waveforms ofthe electrosurgical energy. The electrosurgical system 100 may alsoinclude a plurality of output connectors corresponding to a variety ofelectrosurgical instruments.

The electrosurgical system 100 further includes a monopolarelectrosurgical instrument 120 having an electrode for treating tissueof the patient (e.g., an electrosurgical cutting probe or ablationelectrode) with a return pad 125. The monopolar electrosurgicalinstrument 120 can be connected to the electrosurgical generator 110 viaone of the plurality of output connectors. The electrosurgical generator110 may generate electrosurgical energy in the form of radio frequency(RF) energy. The electrosurgical energy is supplied to the monopolarelectrosurgical instrument 120, which applies the electrosurgical energyto treat the tissue. The electrosurgical energy is returned to theelectrosurgical generator 110 through the return pad 125. The return pad125 provides a sufficient contact area with the patient's tissue so asto minimize the risk of tissue damage due to the electrosurgical energyapplied to the tissue. In addition, the electrosurgical generator 110and the return pad 125 may be configured to monitor tissue-to-patientcontact to ensure that sufficient contact exists between the return pad125 and the patient to minimize the risk of tissue damages.

The electrosurgical system 100 also includes a bipolar electrosurgicalinstrument 130, which can be connected to the electrosurgical generator110 via one of the plurality of output connectors. During operation ofthe bipolar electrosurgical instrument, electrosurgical energy issupplied to one of the two jaw members, e.g., jaw member 132, of theinstrument's forceps, is applied to treat the tissue, and is returned tothe electrosurgical generator 110 through the other jaw member, e.g.,jaw member 134.

The electrosurgical generator 110 may be any suitable type of generatorand may include a plurality of connectors to accommodate various typesof electrosurgical instruments (e.g., monopolar electrosurgicalinstrument 120 and bipolar electrosurgical instrument 130). Theelectrosurgical generator 110 may also be configured to operate in avariety of modes, such as ablation, cutting, coagulation, and sealing.The electrosurgical generator 110 may include a switching mechanism(e.g., relays) to switch the supply of RF energy among the connectors towhich various electrosurgical instruments may be connected. For example,when an electrosurgical instrument 120 is connected to theelectrosurgical generator 110, the switching mechanism switches thesupply of RF energy to the monopolar plug. In embodiments, theelectrosurgical generator 110 may be configured to provide RF energy toa plurality of instruments simultaneously.

The electrosurgical generator 110 includes a user interface havingsuitable user controls (e.g., buttons, activators, switches, or touchscreens) for providing control parameters to the electrosurgicalgenerator 110. These controls allow the user to adjust parameters of theelectrosurgical energy (e.g., the power level or the shape of the outputwaveform) so that the electrosurgical energy is suitable for aparticular surgical procedure (e.g., coagulating, ablating, tissuesealing, or cutting). The electrosurgical instruments 120 and 130 mayalso include a plurality of user controls. In addition, theelectrosurgical generator 110 may include one or more display screensfor displaying a variety of information related to operation of theelectrosurgical generator 110 (e.g., intensity settings and treatmentcomplete indicators). The electrosurgical instruments 120 and 130 mayalso include a plurality of input controls that may be redundant withcertain input controls of the electrosurgical generator 110. Placing theinput controls at the electrosurgical instruments 120 and 130 allows foreasier and faster modification of the electrosurgical energy parametersduring the surgical procedure without requiring interaction with theelectrosurgical generator 110.

FIG. 2A is a block diagram of generator circuitry 200 within theelectrosurgical generator of FIG. 1. The generator circuitry 200includes a low frequency (LF) rectifier 220, a direct current-to-directcurrent (DC/DC) converter 225, an RF amplifier 230, a plurality ofsensors 240, analog-to-digital converters (ADCs) 250, a controller 260,a hardware accelerator 270, a processor subsystem 280, and a userinterface (UI) 290. The generator circuitry 200 is configured to connectto a power source 210, such as a wall power outlet or other poweroutlet, which generates alternating current (AC) having a low frequency(e.g., 25 Hz, 50 Hz, or 60 Hz). The power source 210 provides the ACpower to the LF rectifier 220, which converts the AC to direct current(DC). Alternatively, the power source 210 and the LF rectifier 220 maybe replaced by a battery or other suitable device to provide DC power.

The DC output from the LF rectifier 220 is provided to the DC/DCconverter 225 which converts the DC to a desired level. The converted DCis provided to the RF amplifier 230, which includes a DC-to-AC (DC/AC)inverter 232 and a resonant matching network 234. The DC/AC inverter 232converts the converted DC to an AC waveform having a frequency suitablefor an electrosurgical procedure (e.g., 472 kHz, 29.5 kHz, and 19.7kHz).

The appropriate frequency for the electrosurgical energy may differbased on electrosurgical procedures and modes of electrosurgery. Forexample, nerve and muscle stimulations cease at about 100,000 cycles persecond (100 kHz) above which point some electrosurgical procedures canbe performed safely, i.e., the electrosurgical energy can pass through apatient to targeted tissue with minimal neuromuscular stimulation. Forexample, typically, ablation procedures use a frequency of 472 kHz.Other electrosurgical procedures can be performed at pulsed rates lowerthan 100 kHz, e.g., 29.5 kHz or 19.7 kHz, with minimal risk of damagingnerves and muscles, e.g., Fulgurate or Spray. The DC/AC inverter 232 canoutput AC signals with various frequencies suitable for electrosurgicaloperations.

As described above, the RF amplifier 230 includes a resonant matchingnetwork 234. The resonant matching network 234 is coupled to the outputof the DC/AC inverter 232 to match the impedance at the DC/AC inverter232 to the impedance of the tissue so that there is maximum or optimalpower transfer between the generator circuitry 200 and the tissue.

The electrosurgical energy provided by the DC/AC inverter 232 of the RFamplifier 230 is controlled by the controller 260. The voltage andcurrent waveforms of the electrosurgical energy output from the DC/ACinverter 232 are sensed by the plurality of sensors 240 and provided tothe controller 260, which generates control signals from a DC/DCconverter controller 278, e.g., a pulse width modulator (PWM) or digitalpulse width modulator (DPWM) to control the output of the DC/DCconverter 225 and from a DC/AC inverter controller 276 to control theoutput of the DC/AC inverter 232. The controller 260 also receives inputsignals via the user interface (UI) 290. The UI 290 allows a user toselect a type of electrosurgical procedure (e.g., monopolar or bipolar)and a mode (e.g., coagulation, ablation, sealing, or cutting), or inputdesired control parameters for the electrosurgical procedure or themode. The DC/DC converter 225 of FIG. 2A may be fixed or variabledepending on the power setting or desired surgical effects. When it isfixed, the RF amplifier behaves as a Class S device, which is shown inFIG. 2C. When it is variable, it behaves as a device according to themodified-Kahn technique, which is shown in FIG. 2B.

The plurality of sensors 240 sense voltage and current at the output ofthe RF amplifier 230. The plurality of sensors 240 may include two ormore pairs or sets of voltage and current sensors that provide redundantmeasurements of the voltage and current. This redundancy ensures thereliability, accuracy, and stability of the voltage and currentmeasurements at the output of the RF amplifier 230. In embodiments, theplurality of sensors 240 may include fewer or more sets of voltage andcurrent sensors depending on the application or the design requirements.The plurality of sensors 240 may also measure the voltage and currentoutput from other components of the generator circuitry 200 such as theDC/AC inverter 232 or the resonant matching network 234. The pluralityof sensors 240 may include any known technology for measuring voltageand current including, for example, a Rogowski coil.

The sensed voltage and current waveforms are fed to analog-to-digitalconverters (ADCs) 250. The ADCs 250 sample the sensed voltage andcurrent waveforms to obtain digital samples of the voltage and currentwaveforms. This is also often referred to as an Analog Front End (AFE).The digital samples of the voltage and current waveforms are processedby the controller 260 and used to generate control signals to controlthe DC/AC inverter 232 of the RF amplifier 230 and the DC/DC converter225. The ADCs 250 may be configured to sample the sensed voltage andcurrent waveforms at a sample frequency that is an integer multiple ofthe RF frequency.

As shown in the embodiment of FIG. 2A, the controller 260 includes ahardware accelerator 270 and a processor subsystem 280. As describedabove, the controller 260 is also coupled to a UI 290, which receivesinput commands from a user and displays output and input informationrelated to characteristics of the electrosurgical energy (e.g., selectedpower level). The hardware accelerator 270 processes the output from theADCs 250 and cooperates with the processor subsystem 280 to generatecontrol signals.

The hardware accelerator 270 includes a dosage monitoring and control(DMAC) 272, an inner power control loop 274, a DC/AC inverter controller276, and a DC/DC converter controller 278. All or a portion of thecontroller 260 may be implemented by a field programmable gate array(FPGA), an application specific integrated circuit (ASIC), a digitalsignal processor (DSP), and/or a microcontroller.

The DMAC 272 receives samples of the sensed voltage and currentwaveforms from the ADCs 250 and calculates the average real power andthe real part of the tissue impedance. The DMAC 272 then provides thereal power and the real part of the impedance of the tissue to the innerpower control loop 274, which generates a control signal for the DC/ACinverter controller 276 based on one or more of the real power and thereal part of the impedance of the tissue. The DC/AC inverter controller276 in turn generates a first pulse-width modulation (PWM) controlsignal to control the output of the DC/AC inverter 232.

The processor subsystem 280 includes an outer power control loop 282, astate machine 284, and a power setpoint circuit 286. The processorsubsystem 280 generates a second PWM control signal based on the outputof the DMAC 272 and parameters (e.g., electrosurgical mode) selected bythe user via the UI 290. Specifically, the parameters selected by theuser are provided to the state machine 284 which determines a state ormode of the generator circuitry 200. The outer power control loop 282uses this state information and the output from the DMAC 272 todetermine control data. The control data is provided to the powersetpoint circuit 286, which generates a power setpoint based on thecontrol data. The DC/DC converter controller 278 uses the power setpointto generate an appropriate PWM control signal for controlling the DC/DCconverter 225 to converter the DC output from the LF rectifier 220 to adesired level. If the user does not provide operational parameters tothe state machine 284 via the UI 290, then the state machine 284 maymaintain or enter a default state.

FIG. 3 shows a more detailed diagram of the hardware accelerator 270 ofFIG. 2A. The hardware accelerator 270 implements those functions of thegenerator circuitry 200 that may have special processing requirementssuch as high processing speeds. The hardware accelerator 270 includesthe DMAC 272, the inner power loop control 274, the DC/AC invertercontroller 276, and the DC/DC converter controller 278 shown in FIG. 2A.

The DMAC 272 includes four analog-to-digital converter (ADC) controllers312 a-312 d, a digital signal processor 314, RF data registers 316, andDMAC registers 318. The ADC controllers 312 a-312 d control theoperation of the ADCs 250 (FIG. 2A), which convert sensed voltage andcurrent waveforms into digital data. The digital data is then providedto the digital signal processor 314 that implements various filteringand other digital signal processing functions.

The sensed voltage and current are the digital input to the ADCs 250,which sample the sensed voltage and current. The ADC controllers 312a-312 d provide operational parameters, including a predeterminedsampling rate, to the ADCs 250 so that the ADCs sample the sensedvoltage and current synchronously at a predetermined sampling rate,i.e., a predetermined number of samples per second, or predeterminedsampling period that is coherent with the RF inverter frequency, i.e.,an integer multiple sampling frequency to the RF inverter frequency. TheADC controllers 312 a-312 d control the operation of the ADCs 250, whichconvert sensed voltage and current waveforms into digital data. Thedigital data is then provided to the digital signal processor 314 thatimplements various filtering and other digital signal processingfunctions.

The sensed voltage and current are input to the ADCs 250, which samplethe sensed voltage and current. The ADC controllers 312 a-312 d provideoperational parameters, including a predetermined sampling rate, to theADCs 250 so that the ADCs sample the sensed voltage and currentsynchronously at a predetermined sampling rate, i.e., a predeterminednumber of samples per second, or predetermined sampling period. The ADCcontrollers 312 a-312 d may be configured to control the ADCs 250 sothat the sampling period corresponds to an integer multiple of the RFfrequency of the voltage and current waveforms. This is often referredto as coherent sampling.

The digital data obtained by sampling the voltage and current waveformsis provided to the digital signal processor 314 via the ADC controllers312 a-312 d. The digital signal processor 314 uses the digital data tocalculate a complex voltage V_(comp), a complex current I_(comp), a realpower P_(real), and a real part of the tissue impedance Z_(real).Generally, tissue impedance is real or resistive, but can have a smallcapacitive component after the tissue is “cooked.” Further, a cablebetween the electrosurgical generator and the tissue also has resistiveand reactive components. For these reasons, electrosurgical generatorstypically include controls systems that compensate for these parasiticsto more accurately measure the tissue impedance. These control systems,however, require complex computations that are computationallyinefficient, which results in additional cost to perform the tissueimpedance calculations in a timely manner or at update ratescommensurate to the capabilities of the RF control loop calculations.

In alternative embodiments depicted in FIGS. 2B and 2C, the hardwareaccelerator is not available and many of the primary RF measurement andcontrol functions just described reside instead entirely within aprogrammable device called an application specific standard product(ASSP) integrated circuit that includes at least a DSP core processorand multiple digital pulse width modulators (DPWM) that aresubstantially similar in function to the hardware accelerator and itsDSP and/or microcontroller core.

In other embodiments, there may also be a second microprocessor coreavailable within the ASSP that contains additional ADCs which may beconnected to the sensors for performing the redundant dosage monitoringfunctions separately from the RF control functions. The second processormay also perform user interface functions such as receiving andrequesting power settings, activation requests, and so forth for theuser from the RF controller. The ASSP may also utilize only one RFcontrol loop (or compensator loop), instead of two “inner” and “outer”compensator loops, for controlling directly any of the following: power,voltage, current, temperature, or impedance. This loop may use a singleproportional-integral-derivative compensator that changes between theseprocess variables using bumpless transfer methods and saturable limits.

FIG. 2B shows an electrosurgical system including generator circuitryaccording to the modified-Kahn technique 201. The generator circuitry201 includes an RF amplifier 241 and a controller 251 for controllingthe RF amplifier 241 to deliver electrosurgical energy having desiredcharacteristics to tissue 247 being treated. The RF amplifier 241receives AC or DC from the power source 210. The RF amplifier includesan AC/DC or DC/DC converter 242, which converts the AC or DC provided bythe power source 210 into a suitable level of DC. As in FIG. 2A, the RFamplifier 241 also includes a DC/AC inverter 232 which converts the DCto AC. The RF amplifier 241 also includes a single- or dual-moderesonant matching network 244 and mode relays 248 for switching modes ofthe resonant matching network 244.

The output from the RF amplifier 241 is provided to sensors 246, whichmay include voltage sensors, current sensors, and temperature sensors.The sensor signals output from sensors 246 are provided to thecontroller 251 via an analog front end (AFE) 252 of the controller 251.The AFE conditions and samples the sensor signals to obtain digitalsensor data representing the sensor signals. The controller 251 alsoincludes a signal processor 253, a mode state control and bumplesstransfer unit 254, a compensator or PID controller 255, a pulse widthmodulator (PWM) or digital pulse width modulator (DPWM) 256, and avoltage-controlled oscillator or numerically-controlled oscillator 257.

The signal processor 253 receives the digital sensor data and performsthe calculations and other functions of the systems and methodsaccording to the present disclosure. Among other things, the signalprocessor 253 calculates the real and imaginary parts of the sensedvoltage and current, the impedance, and/or the power, and performsfunctions to control one or more of the voltage, current, power,impedance, and temperature. The signal processor 253 also generates andprovides process variables to the mode state control and bumplesstransfer unit 254 and a compensator or PID controller 255. The modestate control and bumpless transfer unit 254 controls the mode relays248 for the single or dual mode resonant matching network 244 accordingto the tissue effect algorithm, and generates and provides coefficientsand setpoints to the compensator or PID controller 255.

The compensator or PID controller 255 generates controller outputvariables and provides them to the pulse width modulator (PWM) ordigital pulse width modulator (DPWM) 256. The pulse width modulator(PWM) or digital pulse width modulator (DPWM) 256 receives an oscillatorsignal from the voltage-controlled oscillator or thenumerically-controlled oscillator 257 and generates a control signal forcontrolling the AC/DC or DC/DC converter 242. The voltage-controlledoscillator or the numerically-controlled oscillator 257 also generatescontrol signals for controlling the DC/AC inverter 232.

Like the generator circuitry 200 of FIG. 2A, the generator circuitry 201includes a user interface 290 through which a user can control and/ormonitor the functions of the generator circuitry 201 via a controllerapplication interface 258 of the controller 251.

FIG. 2C shows an electrosurgical system including generator circuitryaccording to a Class S device topology 202. Unlike the generatorcircuitry 201 of FIG. 2B, the generator circuitry 202 does not includethe AC/DC or DC/DC Converter 242. An external low-frequency (LF)rectifier 220 or battery provides an appropriate level of DC to theDC/AC Inverter 232 of the RF amplifier 241. As shown in FIG. 2C, the PWMor DPWM 256 receives an oscillator signal from the VCO or NCO 257 andgenerates a control signal for controlling the DC/AC Inverter 232.

The output of the digital signal processor 314 is provided to theprocessor subsystem 280 of FIG. 2A via RF data registers 316 (see FIG.3). The DMAC 272 also includes DMAC registers 318 that receive and storerelevant parameters for the digital signal processor 314 (see FIG. 3).The digital signal processor 314 further receives signals from a PWMmodule 346 of the DC/AC inverter controller 276.

The DMAC 272 provides a control signal to the inner power control loop274 via signal line 321 and to the processor subsystem 280 via signalline 379. The inner power control loop 274 processes the control signaland outputs a control signal to the DC/AC inverter controller 276. Theinner power control loop 274 includes a compensator 326, compensatorregisters 330, and VI limiter 334. The signal line 321 carries andprovides a real part of the impedance to the compensator 326.

When there is a user input, the processor subsystem 280 receives theuser input and processes it with the outputs from the digital signalprocessor 314 via a signal line 379. The processor subsystem 280provides control signals via a compensator registers 330 to a VI limiter334, which corresponds to the power setpoint circuit 286 in FIG. 2A. TheVI limiter 334 then provides a desired power profile (e.g., a minimumand a maximum limits of the power for a set electrosurgical mode oroperation) based on the user input and the output of the digital signalprocessor 314, the compensator registers 330 also provide other controlparameters to the compensator 326, and then the compensator 326 combinesall control parameters from the compensator registers 330 and the VIlimiter 334, to generate output to the DC/AC inverter controller 276 viasignal line 327.

The DC/AC inverter controller 276 receives a control parameter andoutputs control signals that drives the DC/AC inverter 232. The DC/ACinverter controller 276 includes a scale unit 342, PWM registers 344,and the PWM module 346. The scale unit 342 scales the output of thecompensator registers 330 by multiplying and/or adding a number to theoutput. The scale unit 342 receives a number for multiplication and/or anumber for addition from the PWM registers 344 via signal lines, 341 aand 341 b. The PWM registers 344 store several relevant parameters tocontrol the DC/AC inverter 232, e.g., a period, a pulse width, and aphase of the AC signal to be generated by the DC/AC inverter 232 andother related parameters. The PWM registers 344 send signals 345 a-345 dto the PWM module 346. The PWM module 346 receives output from the PWMregisters 344 and generates four control signals, 347 a-347 d, thatcontrol four transistors of the DC/AC inverter 232 of the RF amplifier230 in FIG. 2A. The PWM module 346 also synchronizes its informationwith the information in the PWM registers 344 via a register sync signal347.

The PWM module 346 further provides control signals to the compensator326 of the inner power control loop 274. The processor subsystem 280provides control signals to the PWM module 346. In this way, the DC/ACinverter controller 276 can control the DC/AC inverter 232 of the RFamplifier 230 with integrated internal input (i.e., processed resultsfrom the plurality of sensors by the DMAC 272) and external input (i.e.,processed results from the user input by the processor subsystem 280).

The processor subsystem 280 also sends the control signals to the DC/DCconverter controller 278 via signal line 373. The DC/DC convertercontroller 278 processes the control signals and generates anothercontrol signals so that the DC/DC converter 225 converts direct currentto a desired level suitable for being converted by the RF amplifier 230.The DC/DC converter controller 278 includes PWM registers 352 and a PWMmodule 354. The PWM registers 352 receive outputs from the processorsubsystem 280 via signal line 373 and stores relevant parameters as thePWM registers 344 does. The PWM registers 352 send signals 353 a-353 dto the PWM module 354. The PWM module 354 also sends a register syncsignal to the PWM registers 352 and generates four control signals, 355a-355 d, that control four transistors of the DC/DC converter 225 inFIG. 2A.

FIG. 4 is a circuit diagram 400 illustrating switching in differentresonant components, in accordance with an embodiment of the presentdisclosure. The circuit diagram 400 illustrates mode relays 248 andmatching network 244. The mode relays 248 allow a user to switch betweendifferent operating modes. For example, the top mode relay 248 allows auser to switch between a cut mode and a spray mode, whereas the bottommode relay 248 allows a user to switch between a ligature mode and ablend mode. One skilled in the art may contemplate a plurality of relaysfor switching between a plurality of operating modes. Additionally, thecapacitors 410 and the inductors 420 are appropriately sized for theselected mode. The matching network 244 includes two transformers 430 tovary the relative voltage of the circuit 400 and provide for patientisolation.

The preceding description provides a detailed account of the componentsand devices for controlling the output of an electrosurgical generator110. Typically, the manner in which average power output from a DC/ACinverter (and then applied to a patient) is reduced is by reducing thepulse width of the PWM signal output by the DC/AC inverter controller276 (FIG. 2A). However, power control in this manner can result in aloss of efficiency when operating a low power setting.

FIG. 5A depicts an output signal of the DC/AC inverter controller 276(FIG. 2A) and particularly the PWM module 346 (FIG. 3), which controlthe DC/AC inverter 232. In FIG. 5A, the initial signal is a continuouswave (CW) controlling the DC/AC inverter 232. The pulses (i.e., the highand low signals) of the CW have a short pulse width T_(PW) _(High) . Byshortening the pulse width, the average power output by the DC/ACinverter 232, and ultimately applied to the patient, is reduced. Asnoted above, however, mere reduction in the pulse width when using a CWcan result in efficiency losses as the average power output is reduced.

According to one embodiment of the present disclosure, the efficiency ofthe DC/AC inverter 232 may be increased by lengthening the pulse widthto T_(PW) _(Low) , and transitioning from a CW to a pulsed wave (PW)with a 50% duty cycle. In other words, pulses are only sent to the DC/ACinverter 232 during 50% of a period T. In the example of FIG. 5A, duringthe period T, four cycles of pulsed signals are produced during a periodT_(on) followed by no signal being produced for a period T_(off), whichis also four cycles, thus T_(on) and T_(off) are equal (i.e., representthe same period of time). Further, in this example, by lengthening thepulse width T_(PW) _(Low) to approximately twice T_(PW) _(High) , theaverage power output by the DC/AC inverter 232 may be maintained.However, because of the decrease in the number of switchings that occurat the DC/AC inverter 232, an increase of the time between suchswitchings (i.e., T_(PW) _(Low) >T_(PW) _(High) ), and a period T_(off)where no switchings occur, an increase in efficiency is achieved ascompared to simply reducing the pulse width of a CW.

In an alternative or additional embodiment, the efficiency at low powerlevels may be improved by dropping or deactivating at least somepredetermined integer number of output cycles. As shown in FIG. 5B, theduty cycle of the PW which is supplied to the DC/AC inverter 232 remainsat 50%. However, rather than a PW where a period T_(on) is followed by aperiod T_(off), where periods T_(on) and T_(off) are equal, the periodsof T_(off) may be randomly dispersed in the period T, as represented bythe periods of no signal 510. The aggregate time for the periods of nosignal 510 are equivalent to T_(off) (shown in FIG. 5A), and result inthe same output from the DC/AC inverter, when the amplitude of thecurrent remains constant.

The result of the signaling schemes depicted in FIGS. 5A and 5B is thattwo time parameters are employed in achieving a desired average power.The first is the overall duty cycle (shown as 50%) whereby no signal issupplied during T_(off) or half of the period T. The other is the pulsewidth (e.g., T_(PW) _(Low) ) of the signal supplied during T_(on),resulting in greater control and greater efficiency when low powers aredesired for use by a clinician. As an example, lower power may be 10% ofrated power of the electrosurgical generator 110.

It is noted that the efficiency may be determined by the controller 260.However, in certain circumstances, the efficiency may not be determinedby the controller 260, but with other external efficiency computingcomponents/elements. Reference is made to U.S. Provisional Patent No.61/838,753 entitled “DEAD-TIME OPTIMIZATION OF RESONANT INVERTERS,” theentire contents of which are hereby incorporated by reference, foralternative online and/or offline methods of determining efficiency. Forexample, the efficiency of the system may be characterized offline andthe off cycles may be inserted when a predetermined threshold is reachedfor a control parameter, such as, duty cycle or phase, or when a sensedpower drops below a certain threshold.

Moreover, the dropped cycles, within any given time period, may berandomized by using a pseudo-random sequence determined by a randomnumber generator. The random number generator may be, for example, aGalois sequence that spreads out the spectrum in order to mitigate anyundesirable frequencies. As a result, a useful range of operation of theelectrosurgical generator 110 may be extended, while maintainingreasonable energy conversion efficiency.

It is to be understood that the disclosed embodiments are merelyexemplary of the disclosure, which can be embodied in various forms.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a basis for theclaims and as a representative basis for teaching one skilled in the artto variously employ the present disclosure in virtually anyappropriately detailed structure. Further, the terms and phrases usedherein are not intended to be limiting; but rather, to provide anunderstandable description of the disclosure.

It is to be understood that the terminology used herein is for thepurpose of describing particular embodiments only and is not intended tobe limiting. In this document, the terms “a” or “an”, as used herein,are defined as one or more than one. The term “plurality,” as usedherein, is defined as two or more than two. The term “another,” as usedherein, is defined as at least a second or more. The terms “including”and/or “having,” as used herein, are defined as comprising (i.e., openlanguage). The term “coupled,” as used herein, is defined as connected,although not necessarily directly, and not necessarily mechanically.Relational terms such as first and second, top and bottom, and the likemay be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. The terms“comprises,” “comprising,” or any other variation thereof are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a” does not, without more constraints,preclude the existence of additional identical elements in the process,method, article, or apparatus that comprises the element.

As used herein, the term “about” or “approximately” applies to allnumeric values, whether or not explicitly indicated. These termsgenerally refer to a range of numbers that one of skill in the art wouldconsider equivalent to the recited values (i.e., having the samefunction or result). In many instances these terms may include numbersthat are rounded to the nearest significant figure. In this document,the term “longitudinal” should be understood to mean in a directioncorresponding to an elongated direction of the object being described.Finally, as used herein, the terms “distal” and “proximal” areconsidered from the vantage of the user or surgeon, thus the distal endof a surgical instrument is that portion furthest away from the surgeonwhen in use, and the proximal end is that portion generally closest tothe user.

It will be appreciated that embodiments of the disclosure describedherein may be comprised of one or more conventional processors andunique stored program instructions that control the one or moreprocessors to implement, in conjunction with certain non-processorcircuits and other elements, some, most, or all of the functions ofultrasonic surgical instruments described herein. The non-processorcircuits may include, but are not limited to, signal drivers, clockcircuits, power source circuits, and user input and output elements.Alternatively, some or all functions could be implemented by a statemachine that has no stored program instructions, in one or moreapplication specific integrated circuits (ASICs), in which each functionor some combinations of certain of the functions are implemented ascustom logic, or in a field-programmable gate array (FPGA) enabling theuse of updateable custom logic either by the manufacturer or the user.Of course, a combination of the three approaches could also be used.Thus, methods and means for these functions have been described herein.

From the foregoing, and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications mayalso be made to the present disclosure without departing from the scopeof the same. While several embodiments of the disclosure have been shownin the drawings and/or described herein, it is not intended that thedisclosure be limited thereto, as it is intended that the disclosure beas broad in scope as the art will allow and that the specification beread likewise. Therefore, the above description should not be construedas limiting, but merely as exemplifications of particular embodiments.Those skilled in the art will envision other modifications within thescope and spirit of the claims appended hereto.

The invention claimed is:
 1. A method for controlling an output of anelectrosurgical generator, the method comprising: converting a directcurrent (DC) to an alternating current (AC) using an inverter of theelectrosurgical generator; sensing a current and a voltage at an outputof the inverter; determining a power level based on the sensed voltageand the sensed current; determining a power efficiency of the inverterof the electrosurgical generator based on the determined power level;and inserting a predetermined integer number of off periods having nopulse signals into control signals provided to the inverter when thedetermined power efficiency of the inverter reaches a threshold powerefficiency.
 2. The method according to claim 1, wherein thepredetermined integer number of off periods are inserted at random timeperiods.
 3. The method according to claim 2, wherein the random timeperiods are generated via a pseudo-random sequence determined by arandom number generator.
 4. The method according to claim 1, furthercomprising switching from a continuous wave mode to a pulsed wave mode.5. The method according to claim 1, further comprising determining aduty cycle to maintain the determined power level at a desired powerlevel.
 6. The method according to claim 5, further comprising varyingthe duty cycle to maintain a desired power efficiency.
 7. The methodaccording to claim 1, further comprising determining a pulse width tomaintain the determined power level at a desired power level.
 8. Themethod according to claim 7, further comprising varying the pulse widthto maintain a desired power efficiency.
 9. An electrosurgical generatorcomprising: a radio frequency (RF) amplifier coupled to an electricalenergy source and configured to generate electrosurgical energy, the RFamplifier including: an inverter configured to convert a direct current(DC) to an alternating current (AC); and a plurality of sensorsconfigured to sense voltage and current of the generated electrosurgicalenergy; and a controller coupled to the RF amplifier and the pluralityof sensors, wherein the controller is configured to: determine a powerlevel based on the sensed voltage and the sensed current; determine apower efficiency of the inverter based on the determined power level;and insert a predetermined integer number of off periods having no pulsesignals into control signals provided to the inverter when thedetermined power efficiency of the inverter reaches a threshold powerefficiency.
 10. The electrosurgical generator according to claim 9,wherein the predetermined integer number of off periods are inserted atrandom time periods.
 11. The electrosurgical generator according toclaim 10, wherein the random time periods are generated via apseudo-random sequence determined by a random number generator.
 12. Theelectrosurgical generator according to claim 9, wherein the controlleris further configured to switch from a continuous wave mode to a pulsedwave mode.
 13. The electrosurgical generator according to claim 9,wherein a duty cycle is determined to maintain the determined powerlevel at a desired power level.
 14. The electrosurgical generatoraccording to claim 13, wherein the duty cycle is varied to maintain adesired power efficiency.
 15. The electrosurgical generator according toclaim 9, wherein a pulse width is determined to maintain the determinedpower level at a desired power level.
 16. The electrosurgical generatoraccording to claim 15, wherein the pulse width is varied to maintain adesired power efficiency.